PROJECT SUMMARY On a daily basis, sensory stimuli acquire learned values that inform our essential behaviors. Understanding the neural substrates for the emotional associations of stimuli, sometimes referred to as valence, will yield important insights into a wide range of human conditions. The mammalian olfactory system provides a simple model for understanding the neural mechanisms of stimulus valence. Second order neurons in the olfactory bulb distribute odor information into several secondary structures, including the olfactory tubercle (OT) and piriform cortex (PCX). Odor information at this stage is shaped and later transmitted into tertiary structures involved in reward, emotion, and learning, which in turn provide feedback upon the secondary structures. The present proposal seeks to address fundamental principles of odor valence coding in the OT and PCX, and in doing so will resolve major questions regarding the inter-regional processing and storage of stimulus valence. Experiments will be performed in rodents engaged in an operant olfactory task, along with simultaneous multi- electrode single-unit recordings, and in some cases, neural perturbations using chemical-genetics. Using this approach, we will determine whether secondary structures are specialized to code for odor valence (Aim 1). Next we will exploit the connectivity of secondary olfactory structures to determine the dependence of the OT and PCX upon each other for odor valence coding (Aim 2). Finally, we will determine if and how valence coding in the OT and PCX depends upon top-down modulation by a prominent tertiary association structure with known importance for valence (Aim 3). Together, these investigations will provide fundamental information on the mechanisms of odor information processing, the behavioral relevance of these coding schemes, and the critical interactions between secondary and tertiary olfactory structures.